Why did I get different IQ scores?
A 112 on one site, a 128 on another, a 104 on a third. The spread isn't necessarily a sign that all of them are worthless, but it does show what a score actually depends on.
Different scales, different days
Scores differ because tests vary in content, difficulty, timing, scoring method and the group you're being compared with. Your own state also varies: sleep, attention, motivation and familiarity. Well-constructed tests of the same construct usually correlate substantially with each other, but online tests vary widely in quality, which widens the spread further.
Why two tests give different numbers
| Source of difference | Effect |
|---|---|
| Different abilities sampled | A matrix-only test and a full battery measure different mixes |
| Different norms | Comparison groups differ in age, country and recency |
| Different time limits | Speed matters more in some tests |
| Different scoring | Some scale to 100/15, others use their own scale |
| Measurement error | Every score has a margin |
| Practice | Later tests benefit from familiarity |
| Your state | Rest, stress and focus change performance |
How much variation is normal
On professionally administered tests, a person's scores across instruments typically fall within a moderate range rather than being identical, and reports express this with confidence intervals. Across unstandardized online tests, differences of 15 to 20 points are unsurprising, because the tests aren't measuring on a common scale at all.
Which result to trust
| Test type | Weight to give it |
|---|---|
| Professional, supervised battery | Highest |
| Well-documented online test with explained norms | Moderate |
| Short quiz with no methodology stated | Low |
| Test taken while tired or distracted | Low for that occasion |
| Average of several online tests | Slightly more stable, but still not a real IQ |
Comparing instruments that were never calibrated together
An IQ score is only meaningful relative to the scale and norms of the test that produced it. Comparing numbers from two tests is like comparing measurements from two instruments calibrated differently. Principles for evaluating psychometric tests exist precisely to make such comparisons possible, which is why documentation matters so much.
A sensible approach
- Note which test, which conditions, which day.
- Look for consistent patterns across tests rather than a single number.
- Give the most weight to the best-documented test.
Different score questions
Why are my IQ scores so different?+−
Tests differ in content, norms, timing and scoring, and your condition varies too.
How much can IQ scores vary?+−
Small differences are expected even on good tests; online tests can vary far more.
Should I average my scores?+−
Averaging unstandardized tests doesn't produce a valid IQ estimate.
Which IQ test is the most accurate?+−
Professionally administered batteries with current norms, interpreted by a qualified assessor.
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Explore IQ and reasoning explained
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